Techniques for programming a memory cell

ABSTRACT

Techniques are provided for programming a self-selecting memory cell that stores a first logic state. To program the memory cell, a pulse having a first polarity may be applied to the cell, which may result in the memory cell having a reduced threshold voltage. During a duration in which the threshold voltage of the memory cell may be reduced (e.g., during a selection time), a second pulse having a second polarity (e.g., a different polarity) may be applied to the memory cell. Applying the second pulse to the memory cell may result in the memory cell storing a second logic state different than the first logic state.

CROSS REFERENCE

The present application for patent is a divisional of U.S. patentapplication Ser. No. 16/108,784 by Castro et al., entitled “TECHNIQUESFOR PROGRAMMING A MEMORY CELL,” filed Aug. 22, 2018, assigned to theassignee hereof, and is expressly incorporated by reference in itsentirety herein.

BACKGROUND

The following relates generally to operating a memory array and morespecifically to programming a self-selecting memory device.

Memory devices are widely used to store information in variouselectronic devices such as computers, cameras, digital displays, and thelike. Information is stored by programing different states of a memorydevice. For example, binary devices have two states, often denoted by alogic “1” or a logic “0.” In other systems, more than two states may bestored. To access the stored information, a component of the electronicdevice may read, or sense, the stored state in the memory device. Tostore information, a component of the electronic device may write, orprogram, the state in the memory device.

Various types of memory devices exist, including magnetic hard disks,random access memory (RAM), read only memory (ROM), dynamic RAM (DRAM),synchronous dynamic RAM (SDRAM), ferroelectric RAM (FeRAM), magnetic RAM(MRAM), resistive RAM (RRAM), flash memory, phase change memory (PCM),and others. Memory devices may be volatile or non-volatile. Non-volatilememory cells may maintain their stored logic state for extended periodsof time even in the absence of an external power source. Volatile memorycells may lose their stored state over time unless they are periodicallyrefreshed by an external power source.

Improving memory devices, generally, may include increasing memory celldensity, increasing read/write speeds, increasing reliability,increasing data retention, reducing power consumption, or reducingmanufacturing costs, among other metrics. Programming a memory cellusing a reduced write voltage may be desired to reduce stress on thememory cell and decrease overall power usage of the memory array.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example memory device in accordance with examplesof the present disclosure.

FIG. 2 illustrates an example of a memory array that supports techniquesfor programming a self-selecting memory device in accordance withaspects of the present disclosure.

FIG. 3 illustrates an example of a diagram showing distributions ofthreshold voltages of a self-selecting memory cell that supportstechniques for programming a self-selecting memory device in accordancewith aspects of the present disclosure.

FIG. 4 illustrates examples of a timing diagrams associated withdistributions of threshold voltages of a self-selecting memory cell thatsupports techniques for programming a self-selecting memory device inaccordance with aspects of the present disclosure.

FIG. 5 shows a block diagram of a device that supports techniques forprogramming a self-selecting memory device in accordance with aspects ofthe present disclosure.

FIGS. 6 through 8 illustrate flowcharts of methods that supporttechniques for programming a self-selecting memory device in accordancewith aspects of the present disclosure.

DETAILED DESCRIPTION

A self-selecting memory cell including a chalcogenide alloy may beprogrammed to store one or more bits of data by using variousprogramming pulses. As such, a single self-selecting memory cell may beconfigured to store more than one bit of digital data. In some cases, aself-selecting memory cell may be selected by applying a certain biasbetween a word line and a digit line. The logic state that is stored ina self-selecting memory cell may be based on a polarity of a programmingpulse applied to the self-selecting memory cell. For example, aself-selecting memory may store a logic ‘0’ upon application of aprogramming pulse having a first polarity and the self-selecting memorymay store a logic ‘1’ upon application of a programming pulse having asecond, different polarity. Further, the threshold voltagesrepresentative of a logic state (e.g., a logic “0”) detected by a sensecomponent may vary based on the polarity of the read pulse appliedduring a read operation. For example, the threshold voltages may appeardifferent when applying different polarities of read pulses due to theasymmetrical distribution of ions in a programmed self-selecting memorycell.

Techniques are provided for programming a self-selecting memory cell(e.g., that may include a chalcogenide material) by detecting theoccurrence of a snap-back event. To program (e.g., to write) aself-selecting memory storing a first logic state (e.g., a logic “1”), aprogramming pulse sequence that includes two pulses may be used. A firstpulse of the programming pulse sequence may have a first polarity andthe second pulse of the programming pulse sequence may have a secondpolarity different than the first polarity. Depending on the logic statestored in the self-selecting memory cell, the self-selecting memory cellmay experience a snap-back event as a result of the first pulse beingapplied to the cell. A snapback event may be characterized by anincrease (e.g., sudden increase) in a conductance of the memory cell.After a duration, the memory cell may return to its originalconductance. After the memory cell returns to its original conductance,the memory cell may experience a temporary reduction of its thresholdvoltage.

Upon detecting the snapback event, the second pulse may be applied toprogram a second logic state (e.g., a logic “0”) to the memory cell.Because the threshold voltage of the memory cell may be temporarilyreduced, the second pulse may comprise a lesser magnitude to program thesecond logic state. Stated another way, when a threshold voltage of thememory cell is reduced, a lower voltage is needed to write a secondlogic state to the memory cell (e.g., as opposed to a threshold voltageof the memory cell not being reduced). Thus, by applying a secondvoltage to a self-selecting memory cell during a snapback event (e.g.,during a duration that the threshold voltage of the memory cell isreduced), a logic state may be written to the memory cell using areduced voltage, which may reduce stress of the memory cell and decreaseoverall power consumption of the memory array. In some cases, theduration of the snapback event may be less than 1 nanosecond. If nosnap-back event is detected, the self-selecting memory cell may alreadystore the value attempting to be written to the self-selecting memorycell by the write operation, and the second pulse may not be applied tothe memory cell.

In some examples, a first pulse may be applied to a memory cell storinga first logic state. As described above, the application of the firstpulse may result in a snapback event associated with the memory cell.The snapback event may then be detected (e.g., by a memory controller),and a second pulse may be applied to the memory cell based on or inresponse to the snapback event being detected. In some examples, thesecond pulse may have a second polarity (e.g., an opposite polarity)different than the first polarity. Based on the application of thesecond pulse, a second logic state (e.g., a different logic state) maybe stored in the memory cell.

In another example, a first pulse may be applied to a memory cell duringa write operation. The memory cell may, in some examples, store a firstlogic state. The first logic state (e.g., a logic “1”) may be detected(e.g., by a memory controller) in response to applying the first pulseto the memory cell. After detecting the first logic state, a secondpulse may be applied to the memory cell. In some examples, the secondpulse may have a second polarity (e.g., an opposite polarity) differentthan the first polarity. Based on the application of the second pulse, asecond logic state (e.g., a different logic state) may be stored in thememory cell.

In some examples, a threshold voltage of a memory cell may be reducedfor a duration during a write operation. In some examples, the thresholdvoltage may be reduced based on a first pulse being applied to thememory cell. The first pulse may, for example, have a first polarity andthe memory cell may store a first logic value. During the duration inwhich the threshold voltage of the memory cell is reduced, a secondpulse may be applied to the memory cell. In some examples, the secondpulse may have a different polarity than the first pulse. Based on theapplication of the second pulse, a second logic state (e.g., a differentlogic state) may be stored in the memory cell.

Features of the disclosure introduced above are further described belowin the context of memory array. Specific examples are then described foroperating the memory array related to techniques to program aself-selecting memory device in some examples. These and other featuresof the disclosure are further illustrated by and described withreference to apparatus diagrams, system diagrams, and flowcharts thatrelate to techniques for programming a self-selecting memory device.

FIG. 1 illustrates an example memory device 100 in accordance withexamples of the present disclosure. Memory device 100 may also bereferred to as an electronic memory apparatus. FIG. 1 is an illustrativerepresentation of various components and features of the memory device100. As such, it should be appreciated that the components and featuresof the memory device 100 shown to illustrate functionalinterrelationships, not their actual physical positions within thememory device 100. In the illustrative example of FIG. 1, the memorydevice 100 includes a three-dimensional (3D) memory array 102. The 3Dmemory array 102 includes memory cells 105 that may be programmable tostore different states. In some examples, each memory cell 105 may beprogrammable to store two states, denoted as a logic 0 and a logic 1. Insome examples, a memory cell 105 may be configured to store more thantwo logic states. A memory cell 105 may, in some examples, include aself-selecting memory cell. Although some elements included in FIG. 1are labeled with a numeric indicator, other corresponding elements arenot labeled, though they are the same or would be understood to besimilar, in an effort to increase visibility and clarity of the depictedfeatures.

The 3D memory array 102 may include two or more two-dimensional (2D)memory arrays 103 formed on top of one another. This may increase anumber of memory cells that may be placed or created on a single die orsubstrate as compared with 2D arrays, which in turn may reduceproduction costs, or increase the performance of the memory device, orboth. The memory array 102 may include two levels of memory cells 105and may thus be considered a 3D memory array; however, the number oflevels is not limited to two. Each level may be aligned or positioned sothat memory cells 105 may be aligned (exactly, overlapping, orapproximately) with one another across each level, forming a memory cellstack 145. In some cases, the memory cell stack 145 may include multipleself-selecting memory cells laid on top of another while sharing anaccess line for both as explained below. In some cases, theself-selecting memory cells may be multi-level self-selecting memorycells configured to store more than one bit of data using multi-levelstorage techniques.

In some examples, each row of memory cells 105 is connected to an accessline 110, and each column of memory cells 105 is connected to a bit line115. Access lines 110 and bit lines 115 may be substantiallyperpendicular to one another and may create an array of memory cells. Asshown in FIG. 1, the two memory cells 105 in a memory cell stack 145 mayshare a common conductive line such as a bit line 115. That is, a bitline 115 may be in electronic communication with the bottom electrode ofthe upper memory cell 105 and the top electrode of the lower memory cell105. Other configurations may be possible, for example, a third layermay share an access line 110 with a lower layer. In general, one memorycell 105 may be located at the intersection of two conductive lines suchas an access line 110 and a bit line 115. This intersection may bereferred to as a memory cell's address. A target memory cell 105 may bea memory cell 105 located at the intersection of an energized accessline 110 and bit line 115; that is, access line 110 and bit line 115 maybe energized to read or write a memory cell 105 at their intersection.Other memory cells 105 that are in electronic communication with (e.g.,connected to) the same access line 110 or bit line 115 may be referredto as untargeted memory cells 105.

As discussed above, electrodes may be coupled to a memory cell 105 andan access line 110 or a bit line 115. The term electrode may refer to anelectrical conductor, and in some cases, may be employed as anelectrical contact to a memory cell 105. An electrode may include atrace, wire, conductive line, conductive layer, or the like thatprovides a conductive path between elements or components of memorydevice 100. In some examples, a memory cell 105 may include achalcogenide material positioned between a first electrode and a secondelectrode. One side of the first electrode may be coupled to an accessline 110 and the other side of the first electrode to the chalcogenidematerial. In addition, one side of the second electrode may be coupledto a bit line 115 and the other side of the second electrode to thechalcogenide material. The first electrode and the second electrode maybe the same material (e.g., carbon) or different.

Operations such as reading and writing may be performed on memory cells105 by activating or selecting access line 110 and bit line 115. In someexamples, access lines 110 may also be known as word lines 110, and bitlines 115 may also be known digit lines 115. References to access lines,word lines, and bit lines, or their analogues, are interchangeablewithout loss of understanding or operation. Activating or selecting aword line 110 or a bit line 115 may include applying a voltage to therespective line. Word lines 110 and bit lines 115 may be made ofconductive materials such as metals (e.g., copper (Cu), aluminum (Al),gold (Au), tungsten (W), titanium (Ti)), metal alloys, carbon,conductively-doped semiconductors, or other conductive materials,alloys, compounds, or the like.

Accessing memory cells 105 may be controlled through a row decoder 120and a column decoder 130. For example, a row decoder 120 may receive arow address from the memory controller 140 and activate the appropriateword line 110 based on the received row address. Similarly, a columndecoder 130 may receive a column address from the memory controller 140and activate the appropriate bit line 115. For example, memory array 102may include multiple word lines 110, labeled WL_1 through WL_M, andmultiple digit lines 115, labeled DL_1 through DL_N, where M and Ndepend on the array size. Thus, by activating a word line 110 and a bitline 115, e.g., WL_2 and DL_3, the memory cell 105 at their intersectionmay be accessed.

Upon accessing, a memory cell 105 may be read, or sensed, by sensecomponent 125 to determine the stored state of the memory cell 105. Forexample, a voltage may be applied to a memory cell 105 (using thecorresponding word line 110 and bit line 115) and the presence of aresulting current may depend on the applied voltage and the thresholdvoltage of the memory cell 105. In some cases, more than one voltage maybe applied. Additionally, if an applied voltage does not result incurrent flow, other voltages may be applied until a current is detectedby sense component 125. By assessing the voltage that resulted incurrent flow, the stored logic state of the memory cell 105 may bedetermined. In some cases, the voltage may be ramped up in magnitudeuntil a current flow is detected. In other cases, predetermined voltagesmay be applied sequentially until a current is detected. Likewise, acurrent may be applied to a memory cell 105 and the magnitude of thevoltage to create the current may depend on the electrical resistance orthe threshold voltage of the memory cell 105.

In some examples, a memory cell may be programmed by providing anelectric pulse to the cell, which may include a memory storage element.The pulse may be provided via a first access line (e.g., word line 110)or a second access line (e.g., bit line 115), or a combination thereof.In some cases, upon providing the pulse, ions may migrate within thememory storage element, depending on the polarity of the memory cell105. Thus, a concentration of ions relative to the first side or thesecond side of the memory storage element may be based at least in parton a polarity of a voltage between the first access line and the secondaccess line. In some cases, asymmetrically shaped memory storageelements may cause ions to be more crowded at portions of an elementhaving more area. Certain portions of the memory storage element mayhave a higher resistivity and thus may give rise to a higher thresholdvoltage than other portions of the memory storage element. Thisdescription of ion migration represents an example of a mechanism of theself-selecting memory cell for achieving the results described herein.This example of a mechanism should not be considered limiting. Thisdisclosure also includes other examples of mechanisms of theself-selecting memory cell for achieving the results described herein.

Sense component 125 may include various transistors or amplifiers todetect and amplify a difference in the signals, which may be referred toas latching. The detected logic state of memory cell 105 may then beoutput through column decoder 130 as output 135. In some cases, sensecomponent 125 may be part of a column decoder 130 or row decoder 120.Or, sense component 125 may be connected to or in electroniccommunication with column decoder 130 or row decoder 120. An ordinaryperson skilled in the art would appreciate that sense component may beassociated either with column decoder or row decoder without losing itsfunctional purposes.

A memory cell 105 may be set or written by similarly activating therelevant word line 110 and bit line 115 and at least one logic value maybe stored in the memory cell 105. Column decoder 130 or row decoder 120may accept data, for example input/output 135, to be written to thememory cells 105. In the case of a self-selecting memory cell includinga chalcogenide material, a memory cell 105 may be written to store databy applying a programming sequence including a first pulse having afirst polarity and a second pulse having a second polarity. Theprogramming pulse may have various shapes. This process is discussed inmore detail below with reference to FIGS. 3 and 4.

The memory controller 140 may control the operation (e.g., read, write,re-write, refresh, discharge) of memory cells 105 through the variouscomponents, for example, row decoder 120, column decoder 130, and sensecomponent 125. In some cases, one or more of the row decoder 120, columndecoder 130, and sense component 125 may be co-located with the memorycontroller 140. Memory controller 140 may generate row and columnaddress signals to activate the desired word line 110 and bit line 115.Memory controller 140 may also generate and control various voltages orcurrents used during the operation of memory device 100.

The memory controller 140 may be configured to execute a write operationthat can program a self-selecting memory cell. For example, the memorycontroller 140 may be configured to apply, during a write operation, afirst pulse having a first polarity to the memory cell 105. In someexamples, applying the first pulse having the first polarity may includeapplying a first voltage to the first access line (e.g., to word line110) and a second voltage to the second access line (e.g., bit line115). Applying the second pulse having the second polarity may includeapplying a third voltage to the first access line (e.g., to bit line115) and fourth voltage to the second access line (e.g., bit line 115).The memory controller 140 may be configured to detect a snapback eventat the memory cell 105 in response to applying the first pulse. Thesnapback event may, for example, result in a reduced threshold voltageof the memory cell 105.

In some examples, the memory controller 140 may apply a second pulsehaving a second polarity different than the first polarity to the memorycell 105 in response to detecting the snapback event and, subsequently,may store a second logic state different than the first logic state inthe memory cell 105 based at least in part on applying the second pulseto the memory cell. Stated another way, a threshold voltage of thememory cell 105 may be reduced after applying the first pulse (e.g.,during a snapback event) and applying the second pulse when thethreshold voltage is reduced may store (e.g., write) a second logicstate to the memory cell 105.

In some examples, the memory controller 140 may be configured to apply,during a write operation, a first pulse having a first polarity to thememory cell 105. In some examples, the memory controller 140 may detectthe first logic state stored by the memory cell in response to applyingthe first pulse to the memory cell. As described above, the first logicstate may be detected during a snapback event. In some examples, thememory controller 140 may then store a second logic state in the memorycell 105 by applying a second pulse having a second polarity during thewrite operation based at least in part detecting the first logic state.The second logic state may be different than the first logic state.

FIG. 2 illustrates an example of a 3D memory array 200 that supportstechniques for programming a self-selecting memory device in accordancewith aspects of the present disclosure. Memory array 200 may be anexample of portions of memory array 102 described with reference toFIG. 1. Memory array 200 may include a first array or deck 205 of memorycells that is positioned above a substrate 204 and second array or deck210 of memory cells on top of the first array or deck 205. Memory array200 may also include word line 110-a and word line 110-b, and bit line115-a, which may be examples of word line 110 and bit line 115, asdescribed with reference to FIG. 1. Memory cells of the first deck 205and the second deck 210 each may have one or more self-selecting memorycell (e.g., self-selecting memory cell 220-a and self-selecting memorycell 220-b, respectively). Although some elements included in FIG. 2 arelabeled with a numeric indicator, other corresponding elements are notlabeled, though they are the same or would be understood to be similar,in an effort to increase visibility and clarity of the depictedfeatures.

Self-selecting memory cells of the first deck 205 may include firstelectrode 215-a, chalcogenide material 220-a, and second electrode225-a. In addition, self-selecting memory cells of the second deck 210may include a first electrode 215-b, chalcogenide material 220-b, andsecond electrode 225-b. The self-selecting memory cells of the firstdeck 205 and second deck 210 may, in some examples, have commonconductive lines such that corresponding self-selecting memory cells ofeach deck 205 and 210 may share bit lines 115 or word lines 110 asdescribed with reference to FIG. 1. For example, first electrode 215-bof the second deck 210 and the second electrode 225-a of the first deck205 may be coupled to bit line 115-a such that bit line 115-a is sharedby vertically adjacent self-selecting memory cells.

The architecture of memory array 200 may be referred to as a cross-pointarchitecture, in some cases, in which a memory cell is formed at atopological cross-point between a word line and a bit line asillustrated in FIG. 2. Such a cross-point architecture may offerrelatively high-density data storage with lower production costscompared to other memory architectures. For example, the cross-pointarchitecture may have memory cells with a reduced area and, resultantly,an increased memory cell density compared to other architectures. Forexample, the architecture may have a 4F2 memory cell area, where F isthe smallest feature size, compared to other architectures with a 6F2memory cell area, such as those with a three-terminal selectioncomponent. For example, DRAM may use a transistor, which is athree-terminal device, as the selection component for each memory celland may have a larger memory cell area compared to the cross-pointarchitecture.

While the example of FIG. 2 shows two memory decks, other configurationsare possible. In some examples, a single memory deck of self-selectingmemory cells may be constructed above a substrate 204, which may bereferred to as a two-dimensional memory. In some examples, a three orfour memory decks of memory cells may be configured in a similar mannerin a three-dimensional cross point architecture.

In some examples, one or more of the memory decks may include aself-selecting memory cell 220 that includes chalcogenide material. Theself-selecting memory cell 220 may, for example, include a chalcogenideglass such as, for example, an alloy of selenium (Se), tellurium (Te),arsenic (As), antimony (Sb), carbon (C), germanium (Ge), and silicon(Si). In some example, a chalcogenide material having primarily selenium(Se), arsenic (As), and germanium (Ge) may be referred to as SAG-alloy.In some examples, SAG-alloy may include silicon (Si) and suchchalcogenide material may be referred to as SiSAG-alloy. In someexamples, the chalcogenide glass may include additional elements such ashydrogen (H), oxygen (O), nitrogen (N), chlorine (CO, or fluorine (F),each in atomic or molecular forms.

In some examples, a self-selecting memory cell 220 includingchalcogenide material may be programmed to a logic state by applying afirst pulse having a first polarity. By way of example, when aparticular self-selecting memory cell 220 is programed, elements withinthe cell separate, causing ion migration. Ions may migrate towards aparticular electrode, depending on the polarity of the pulse applied tothe memory cell. For example, in a self-selecting memory cell 220, ionsmay migrate towards the negative electrode. The memory cell may then beread by applying a voltage across the cell to sense. The thresholdvoltage seen during a read operation may be based on the distribution ofions in the memory cell and the polarity of the read pulse. For example,if a memory cell has a given distribution of ions, the threshold voltagedetected during the read operation may be different for a first readpulse with a first polarity than it is with a second read pulse having asecond polarity. Depending on the polarity of the memory cell, thisconcentration of migrating ions may represent a logic “1” or logic “0”state. This description of ion migration represents an example of amechanism of the self-selecting memory cell for achieving the resultsdescribed herein. This example of a mechanism should not be consideredlimiting. This disclosure also includes other examples of mechanisms ofthe self-selecting memory cell for achieving the results describedherein.

Before programming, the self-selecting memory cell 220 may have stored afirst logic state (e.g., a logic “1”). The first pulse may be appliedto, for example, word line 110-b. Upon applying the first pulse, asnapback event at the self-selecting memory cell 220 may be detected inresponse to applying the first pulse. As described above, a snapbackevent may be characterized by a reduced threshold voltage of theself-selecting memory cell 220. For example, as part of a snapback eventthe memory cell may experience an increase (e.g., sudden increase) in aconductance of the memory cell. After a duration, the memory cell mayreturn to its original conductance. After the memory cell returns to itsoriginal conductance, the memory cell may then experience a temporaryreduction of its threshold voltage. This reduction of the threshold maybe detectable using pulses having a positive polarity or a negativepolarity. Thus, applying the first pulse may reduce a threshold voltageof the self-selecting memory cell 220 (e.g., for a duration). In someexamples, the snapback event may be detected by a memory controller(e.g., by memory controller 140 as described above with reference toFIG. 1). After detecting the snapback event, a second pulse having asecond polarity different than the first polarity may be applied to theself-selecting memory cell 220. In some examples, the second pulse maybe applied to bit line 115-b. Once the second pulse with a secondpolarity (e.g., a different polarity) is applied a second logic state(e.g., a logic “0”) may be stored in the self-selecting memory cell 220.

FIG. 3 illustrates an example of a diagram 300 showing distributions ofthreshold voltages of a self-selecting memory cell in accordance withexamples of the present disclosure. A self-selecting memory cell may beconfigured to store a particular logic state based on one or more pulsesapplied to the cell. The voltage distributions depict logic states thatmay be stored in a self-selecting memory cell.

Self-selecting memory cells may include a chalcogenide material asdescribed with reference to FIGS. 1 and 2. The threshold voltagedistributions may represent a programming scheme for writing a logicstate to the cell. The x-axes 305 and 305-a may represent a voltagevalues for threshold voltage distributions of a memory cell (e.g.,memory cell 105 as described with reference to FIG. 1). The y-axis 310may represent a likelihood that a threshold voltage may occur in thememory cell. Additionally or alternatively, FIG. 3 may include thresholdvoltage distribution 315 that represents a first logic state and athreshold voltage distribution 320 that represents a second (e.g., adifferent) logic state. In some examples, FIG. 3 may include thresholdvoltage distribution 325 that represents a first logic state andthreshold voltage distribution that represents a second (e.g., adifferent) logic state. In some examples, FIG. 3 may include voltagelevels 335, 340, 345, and 350 which may represent various voltage levelsneeded to access (e.g., write or read) a particular logic state to thememory cell.

In some examples, a write operation 360 may be illustrated. In a firstwrite operation 360, a self-selecting memory cell may be written usingprogramming pulse having a first polarity and a first magnitude. Theprogramming pulse may be configured to store a specific logic state(e.g., a logic “0”) in the memory cell. For example, the programmingpulse may have the voltage level 345 when storing a logic “0” in thememory cell. After applying the voltage 350, the memory component of thememory cell may have an asymmetric distribution of a material (e.g.,ions) that is configured to store the logic state. Due to the asymmetricdistribution, the threshold voltage observed by a sense component for aspecific logic state may be different based on the polarity of the readpulse applied to the memory cell. For example, if a first read pulsehaving a first polarity is applied to the memory cell, the memory cellmay exhibit threshold voltage distributions indicated by the group 365.In another example, if a second read pulse having a second polarity isapplied to the memory cell, the memory cell may exhibit thresholdvoltage distributions indicated by the group 370.

For example, before write operation 360 occurs the memory cell may storelogic state (e.g., a logic “1”). Due to the write operation 360, a logicstate (e.g., a logic “0”) may be written to the memory cell. The memorycell may include a threshold voltage distribution for each logic state(e.g., threshold voltage distributions 320 or 330 for a logic “1”). Towrite the desired logic state to the memory cell, a particular voltagemay be applied to the memory cell to overcome the threshold voltage ofthe memory cell. As shown in FIG. 3, a voltage 350 may be used to writea logic “1” to the memory cell in some write operations. Accordingly,the voltage 350 (e.g., VWRT1) may be applied to the memory cell to storea logic “1” in the memory cell for a duration. Because voltage 350 is ahigher voltage (e.g., relative to voltage 340), the memory cell mayultimately endure higher stress and the memory array (e.g., memory array102 as described with reference to FIG. 1) associated with the memorycell may consume less power.

In some examples, a write operation 355 may be illustrated. The writeoperation 355 may reduce stress on a memory cell and may result in thememory array associated with the memory cell consuming less power (e.g.,relative to write operation 360). In the write operation 355, a desiredlogic state may be written to a memory cell that already stores acurrent logic state. For example, the current logic state of the memorycell may be a logic “1,” as represented by threshold voltagedistributions 320 or 330, and the desired logic state may be a logic“0,” as represented by threshold voltage distributions 315 or 325. Towrite the desired logic state (e.g., a logic “0”) to the memory cell, afirst pulse having a first polarity and a first magnitude (e.g., voltage340) may be applied to the memory cell. As described above, the memorycell may include a particular threshold voltage distribution. Byapplying the first pulse to the memory cell, a snapback event may occur.The snapback event may be characterized by a reduction in the thresholdvoltage distribution associated with logic state. Stated another way, byapplying the first pulse to the memory cell, the threshold voltagedistribution associated with logic state may shift (e.g., towards OV).When the snap event occurs, the distributions 315, 320, 325, or 330 mayshift closer to the y-axis 310 for a duration. After the sudden movementinto the y-axis 310, the distributions 315, 320, 325, and 330 may relaxback out to their original positions. The write operation 355 may beconfigured to write a cell of the opposite polarity before at least oneof the distributions 315, 320, 325, 330 fully recover to their originalpositions.

The occurrence of the snapback that results from applying the voltage340 may indicate that a logic “1” as represented by threshold voltagedistribution 320 is stored in the memory cell. Rather than applying aprogramming pulse of a greater magnitude to write a logic “0,” thememory controller may reverse the polarity of the programming pulse(e.g., the memory controller may apply a programming pulse having anopposite polarity of a pulse associated with the state stored on thememory cell). Thereby taking advantage of the asymmetrical properties ofa programming self-selecting memory cell. Such features may reduce thepower consumed during the write operation 355 as compared to the writeoperation 360.

Because the snapback event results in a reduced voltage distribution ofthe memory cell, a lower voltage may be used to write a logic state tothe memory cell (e.g., relative to write operation 360). Thus, in someexamples, a voltage greater than the threshold distribution of thememory cell may be applied to write logic state to the memory cell.Using a lower voltage may ultimately reduce stress on the memory celland reduce the power consumption of the memory array (e.g., memory array102 as described with reference to FIG. 1) associated with the memorycell.

In some examples, an alternative write operation 355 may be illustrated.The write operation 355 may reduce stress on a memory cell and mayresult in the memory array associated with the memory cell consumingless power (e.g., relative to write operation 360). In the alternativewrite operation 355, a desired logic state may be written to a memorycell that already stores a current logic state. For example, the currentlogic state of the memory cell may be a logic “0,” as represented bythreshold voltage distributions 315 or 325, and the desired logic statemay be a logic “1” as represented by threshold voltage distributions 320or 330.

To write the desired logic state (e.g., a logic “1”) to the memory cell,a first pulse having a first polarity and a first magnitude (e.g.,voltage 335) may be applied to the memory cell. As described above, thememory cell may include a particular threshold voltage distribution. Byapplying the first pulse to the memory cell, a snapback event may occur.The snapback event may be characterized by a reduction in the thresholdvoltage distribution associated with logic state. Stated another way, byapplying the first pulse to the memory cell, the threshold voltagedistribution associated with logic state may shift (e.g., towards OV).

The occurrence of the snapback that results from applying the voltage335 may indicate that a logic “0” as represented by threshold voltagedistribution 315 is stored in the memory cell. Rather than applying aprogramming pulse of a greater magnitude to write a logic “1,” thememory controller may reverse the polarity of the programming pulse(e.g., the memory controller may apply a programming pulse having anopposite polarity of a pulse associated with the state stored on thememory cell). Thereby taking advantage of the asymmetrical properties ofa programming self-selecting memory cell. Such features may reduce thepower consumed during the write operation 355 as compared to the writeoperation 360.

Because the snapback event results in a reduced voltage distribution ofthe memory cell, a lower voltage may be used to write a logic state tothe memory cell (e.g., relative to write operation 360). Thus, in someexamples, a voltage greater than the threshold distribution of thememory cell may be applied to write logic state to the memory cell.Using a lower voltage may ultimately reduce stress on the memory celland reduce the power consumption of the memory array (e.g., memory array102 as described with reference to FIG. 1) associated with the memorycell.

FIG. 4 illustrates examples of timing diagrams 400 associated withdistributions of threshold voltages of a self-selecting memory cell inaccordance with examples of the present disclosure. A self-selectingmemory cell may be configured to store a particular logic state based onone or more pulses applied to the cell. The voltage distributions depictlogic states that may be stored in a self-selecting memory cell.

Self-selecting memory cells may include a chalcogenide material asdescribed with reference to FIGS. 1 and 2. The threshold voltagedistributions may represent various logic states of a memory cell duringa write operation. In the example of FIG. 4, the timing diagram 405 mayrepresent writing a second logic state (e.g., a logic “1”) to a memorycell that stores a first logic state (e.g., a logic “0”). Timing diagram410 may represent a write operation where a memory cell stores a samelogic state (e.g., a logic “1”) as the logic state desired from a writeoperation (e.g., a logic “1”). Timing diagram 415 may represent a writeoperation where a memory cell stores a same logic state (e.g., a logic“0”) as the logic state desired from a write operation (e.g., a logic“0”). Timing diagram 420 may represent writing a second logic state(e.g., a logic “0”) to a memory cell that stores a first logic state(e.g., a logic “1”).

Timing diagram 405 may depict a write operation of a memory cell (e.g.,of a self-selecting memory cell). Timing diagram 405 may show thevoltage 435, which may be referred to as first pulse 435, and voltage440 (e.g., VHOLD), which may be referred to as second pulse 440. Firstpulse 435 may be an example of voltage 335 as described with referenceto FIG. 3, and second pulse 440 may be an example of voltage 340 asdescribed with reference to FIG. 3, in some cases. Timing diagram 405may also depict the voltage 425 of an access line (e.g., word line 110as described with reference to FIG. 1), and the voltage 430 of an accessline (e.g., bit line 115 as described with reference to FIG. 1).Accordingly, to conduct a write operation on a memory cell, a firstpulse 425 may be applied to one access line and a second pulse 430 maysubsequently be applied to a second access line.

A memory cell associated with timing diagram 405 may store a first logicstate (e.g., a logic “0”). As described above with reference to FIG. 3,to write a second logic state (e.g., a logic “1”) to the memory cell, afirst pulse 435 may be applied to the memory cell. The first pulse 435may be configured such that a snapback event occurs if the memory cellstores a first logic state but that no snapback event occurs if thememory cell stores a second logic state different than the first logicstate. Accordingly, first pulse 435 may be applied to the cell with afirst polarity.

After applying the first pulse 435, a snapback event may occur which maybe characterized by the threshold voltage distribution of the memorycell being reduced. In some examples the snapback event may bedetermined by a memory controller (e.g., memory controller 140 asdescribed with reference to FIG. 1). The snapback event may cause thethreshold voltage associated with the memory cell to be reduced. In somecases, the snapback event may cause the magnitude of the first pulse tobe reduced, as shown by the first pulse 435-a.

A snapback event may occur for a fixed duration, and may be followed bya period in which the memory cell is maintained in a higher conductancestate (e.g., duration 447). This high conductance state may be referredto as a selection time. Thus, to write a second logic value (e.g., alogic “1”) to the memory cell, a second pulse 440 may be applied. Insome cases, the second pulse 440 may be similar to the first pulse435-a, but with a reversed polarity. To reverse the polarity, thevoltages applied to the word line and the bit line may be switched. Asdescribed with reference to FIG. 3, the second pulse 440 may be appliedto the memory cell with a second polarity (e.g., a different polarity).Stated another way, the second pulse 440 may be applied to a respectiveaccess line. By applying the second pulse 440 during the selection time(e.g., during duration 447), a second logic state (e.g., a logic “1”)may written to the memory cell using a reduced voltage as compared tosome write operations. As described above, a lower voltage mayultimately reduce stress on the memory cell and reduce the powerconsumption of the memory array (e.g., memory array 102 as describedwith reference to FIG. 1) associated with the memory cell.

In some examples, the second pulse 440 may not be applied during theselection time (e.g., duration 447). Accordingly a threshold voltage ofthe memory cell may increase to its original level. For example, in thecontext of timing diagram 405, if second pulse 440 were not appliedduring duration 447, a threshold voltage of the memory cell may increaseto the voltage value depicted prior to duration 447. If the second pulse440 were to be applied after the duration 447, for example, themagnitude of the pulse may be greater to achieve the same result ofwriting the logic state to the memory cell. In some examples, the memorycell may be selected after duration 447 by applying a voltage lower thanthe original threshold voltage of the memory cell. For example, athreshold refresh operation may occur by selecting the memory cell afterduration 447 in either polarity without completing the write operation.Because the threshold recovery time of the memory cell may be large(e.g., relative to duration 447) after duration 447, the memory cell maybe deselected (e.g., by applying a same voltage to the word line and tothe digit line of the memory cell). When deselected, additional snapbackevents or other array operations may be conducted on other portions ofthe memory array before completing the write operation depicted bytiming diagram 405. This may enable more efficient writes by effectivelygrouping together multiple cells for some phases of the write operation.

Timing diagram 410 may depict a portion of a write operation of a memorycell (e.g., of a self-selecting memory cell). Timing diagram 410 mayshow a first pulse 435-b being applied to the memory cell. First pulse435-a may be an example of voltage 335 as described with reference toFIG. 3. Timing diagram 410 may also depict the voltage 425-a of accessline (e.g., word line 110 as described with reference to FIG. 1), andthe voltage 430-a of access line (e.g., bit line 115 as described withreference to FIG. 1).

A memory cell associated with timing diagram 410 may store a logic state(e.g., a logic “1”). As described above with reference to FIG. 3, towrite a logic state (e.g., a logic “1”) to the memory cell, a firstpulse 435-a may be applied to the memory cell. Accordingly, first pulse435-a may be applied to the cell with a first polarity.

As described above, when a memory cell stores a first logic state (e.g.,a logic “0”), a snapback event may occur when writing a second logicstate (e.g., a logic “1”) to the memory cell. However, when writing(e.g., attempting to write) a same logic state to a memory cell as thememory cell currently stores, a snapback event may not occur. Statedanother way, when a memory cell stores a logic “1,” and a logic “1” isattempted to be written to the same cell, a snapback event may notoccur. Accordingly, as illustrated in timing diagram 410, a snapbackevent does not occur and the write operation (e.g., the attempted writeoperation) may be complete. The lack of an occurrence of the snapbackevent may be detected by not seeing a reduction in the magnitude of thefirst pulse 435-b. If no snapback is detected, the polarity of theprogramming pulse is not reversed as is shown in timing diagram 405.

Timing diagram 415 may depict a portion of a write operation of a memorycell (e.g., of a self-selecting memory cell). Timing diagram 415 mayshow a first pulse 445 being applied to the memory cell. First pulse 445may be an example of voltage 340 as described with reference to FIG. 3.Timing diagram 415 may also depict the voltage 430-b of an access line(e.g., word line 110 as described with reference to FIG. 1), and thevoltage 425-b of a second access line (e.g., bit line 115 as describedwith reference to FIG. 1).

A memory cell associated with timing diagram 415 may store a logic state(e.g., a logic “0”). As described above with reference to FIG. 3, towrite a logic state (e.g., a logic “0”) to the memory cell, a firstpulse 445 may be applied to the memory cell. Accordingly, first pulse445 may be applied to the cell with a first polarity. As describedabove, when a memory cell stores a first logic state (e.g., a logic“1”), a snapback event may occur when writing a second logic state(e.g., a logic “0”) to the memory cell.

However, when writing (e.g., attempting to write) a same logic state toa memory cell as the memory cell currently stores, a snapback event maynot occur. Stated another way, when a memory cell stores a logic “0,”and a logic “0” is attempted to be written to the same cell, a snapbackevent may not occur. Accordingly, as illustrated in timing diagram 415,a snapback event does not occur and the write operation (e.g., theattempted write operation) may be complete. The lack of an occurrence ofthe snapback event may be detected by not seeing a reduction in themagnitude of the first pulse 445. If no snapback is detected, thepolarity of the programming pulse is not reversed as is shown in timingdiagram 405.

Timing diagram 420 may depict a write operation of a memory cell (e.g.,of a self-selecting memory cell). Timing diagram 420 may show voltage445, which may be referred to as first pulse 445, and voltage 450 (e.g.,VHOLD), which may be referred to as second pulse 450. First pulse 445may be an example of voltage 335 as described with reference to FIG. 3,and second pulse 450 may be an example of voltage 340 as described withreference to FIG. 3, in some cases. Timing diagram 420 may also depictthe voltage 430-c of an access (e.g., word line 110 as described withreference to FIG. 1), and the voltage 425-c of a second access line(e.g., bit line 115 as described with reference to FIG. 1). Accordingly,to conduct a write operation on a memory cell, a first pulse 445-a maybe applied to one access line and a second pulse 450 may subsequently beapplied to a second access line.

A memory cell associated with timing diagram 420 may store a first logicstate (e.g., a logic “1”). As described above with reference to FIG. 3,to write a second logic state (e.g., a logic “0”) to the memory cell, afirst pulse 445-a may be applied to the memory cell. The first pulse445-a may be configured such that a snapback event occurs if the memorycell stores a first logic state but that no snapback event occurs if thememory cell stores a second logic state different than the first logicstate. Accordingly, first pulse 445-a may be applied to the cell with afirst polarity.

After applying the first pulse, a snapback event may occur which may becharacterized by the threshold voltage distribution of the memory cellbeing reduced. In some examples the snapback event may be determined bya memory controller (e.g., memory controller 140 as described withreference to FIG. 1). The snapback event may cause the threshold voltageassociated with the memory cell to be reduced. In some cases, thesnapback event may cause the magnitude of the first pulse to be reduced,as shown by the second pulse 450.

A snapback event may occur for a fixed duration, and may be followed bya period in which the memory cell is maintained in a higher conductancestate (e.g., duration 447-a). This high conductance state may bereferred to as a selection time. Thus, to write a second logic value(e.g., a logic “1”) to the memory cell, a second pulse 440-a may beapplied. In some cases, the second pulse 450 may be similar to the firstpulse 445-a, but with a reversed polarity. To reverse the polarity, thevoltages applied to the word line and the bit line may be switched. Asdescribed with reference to FIG. 3, the second pulse may be applied tothe memory cell with a second polarity (e.g., a different polarity).Stated another way, the second pulse 450 may be applied to the secondaccess line access line. By applying the second pulse 450 during theselection time (e.g., during duration 447-a), a second logic state(e.g., a logic “1”) may written to the memory cell using a reducedvoltage as compared to some write operations. As described above, alower voltage may ultimately reduce stress on the memory cell and reducethe power consumption of the memory array (e.g., memory array 102 asdescribed with reference to FIG. 1) associated with the memory cell.

In some examples, the second pulse 450 may not be applied during theselection time (e.g., duration 447-a). Accordingly a threshold voltageof the memory cell may increase to its original level. For example, inthe context of timing diagram 420, if second pulse 450 were not appliedduring duration 447-a, a threshold voltage of the memory cell mayincrease to the voltage value depicted prior to duration 447-a. If thesecond pulse 450 were to be applied after the duration 447-a, forexample, the magnitude of the pulse may be greater to achieve the sameresult of writing the logic state to the memory cell.

FIG. 5 shows a block diagram 500 of a snapback event detector 505 thatsupports techniques for programming a memory cell in accordance withexamples of the present disclosure. The snapback event detector 505 maybe an example of aspects of a memory controller (e.g., memory controller140 as described with reference to FIG. 1. The snapback event detector505 may include application component 510, detection component 515,storing component 520, selecting component 525, reduction component 530,determination component 535, biasing component 540, and timing component545. Each of these components may communicate, directly or indirectly,with one another (e.g., via one or more buses).

Application component 510 may apply, during a write operation, a firstpulse having a first polarity to a memory cell storing a first logicstate. In some examples, application component 510 may apply a secondpulse having a second polarity different than the first polarity to thememory cell in response to detecting the snapback event. In someexamples, application component 510 may apply a first voltage to a firstaccess line coupled with the memory cell. In some examples, applicationcomponent 510 may apply a second voltage to a second access line coupledwith the memory cell, wherein applying the first pulse is based at leastin part on applying the first voltage and the second voltage.

In some examples, application component 510 may apply the second voltageto the first access line. In some examples, application component 510may apply the first voltage to the second access line, wherein applyingthe second pulse is based at least in part on applying the first voltageto the second access line and the second voltage to the first accessline. In some examples, application component 510 may apply the secondpulse to the memory cell during the duration when the threshold voltageis reduced. In some examples, application component 510 may apply,during a write operation, a first pulse having a first polarity to amemory cell storing a first logic state. In some examples, applicationcomponent 510 may apply a first voltage to a first access line coupledwith the memory cell. In some examples, application component 510 mayapply a second voltage to a second access line coupled with the memorycell, wherein applying the first pulse is based at least in part onapplying the first voltage and the second voltage.

In some examples, application component 510 may apply, during theduration, a second pulse to the memory cell during the write operation,the second pulse having a second polarity different than the firstpolarity. In some examples, application component 510 may apply a firstpulse having a voltage across the memory cell in a first direction and asecond pulse having a voltage across the memory cell in a seconddirection. In some examples, application component 510 may apply, duringa write operation, a first pulse having a first polarity to the memorycell. In some examples, application component 510 may apply a secondpulse having a second polarity different than the first polarity to thememory cell in response to detecting the snapback event.

In some examples, application component 510 may apply the second pulsehaving the second polarity by applying a voltage to the second accessline, the voltage being greater than the reduced threshold voltage. Insome examples, application component 510 may apply the first pulsehaving the first polarity to the memory cell during a duration. In someexamples, application component 510 may apply the first pulse having thefirst polarity by applying a first voltage to the first access line. Insome examples, application component 510 may apply the second pulsehaving the second polarity by applying a second voltage to the secondaccess line, wherein writing the second logic state to the memory cellis based at least in part on a magnitude of the second voltage exceedinga threshold voltage of the memory cell.

Detection component 515 may detect. a snapback event at the memory cellin response to applying the first pulse. Detection component 515 maydetect a reduction in a magnitude of a voltage across the memory cell,wherein detecting the snapback event is based at least in part ondetecting the reduction in the magnitude of the voltage. Detectioncomponent 515 may detect the snapback event based at least in part on avalue of the first logic state being different than the value of thesecond logic state to be stored to the memory cell. Detection component515 may detect a second snapback event at the memory cell in response toapplying the second pulse to the memory cell after the duration.

Detection component 515 may detect the first logic state stored by thememory cell in response to applying the first pulse to the memory cell.Detection component 515 may detect the first logic state based at leastin part on a threshold voltage of the memory cell being less than amagnitude of the first pulse. Detection component 515 may detect thefirst logic state during a duration after applying the first pulse, andwherein the second logic state is written to the memory cell during theduration. In some examples, detection component 515 may detect thesnapback event at the memory cell during a duration after applying thefirst pulse. Detection component 515 may detect the first logic stateduring the duration and the second logic state is written to the memorycell during the duration.

Storing component 520 may store a second logic state different than thefirst logic state in the memory cell based at least in part on applyingthe second pulse to the memory cell. In some examples, storing component520 may store a second logic state in the memory cell by applying asecond pulse having a second polarity during the write operation inresponse to detecting the first logic state, wherein the second logicstate is different than the first logic state. Storing component 520 maystore the second logic state to the memory cell based at least in parton a threshold voltage of the memory cell being reduced for a duration.In some examples, storing component 520 may store a second logic valuein the memory cell after applying the second pulse.

Selecting component 525 may select a voltage magnitude of the firstpulse based at least in part on a value of the second logic state to bestored to the memory cell. In some examples, selecting component 525 mayselect the first pulse from a plurality of pulses based at least in parton a value of the second logic state to be written to the memory cell.

Reduction component 530 may reduce, for a duration, a threshold voltageof a memory cell during a write operation by applying a first pulse tothe memory cell having a first polarity, the memory cell comprising afirst logic value. In some examples, reduction component 530 may reduce,after the duration, the threshold voltage of the memory cell during thewrite operation by applying the first pulse to the memory cell havingthe first polarity, the memory cell comprising the second logic value.

Determination component 535 may determine the first logic value of thememory cell based at least in part on reducing the threshold voltage ofthe memory cell during the write operation.

FIG. 6 shows a flowchart illustrating a method 600 that supportstechniques for programming memory cell in accordance with aspects of thepresent disclosure. The operations of method 600 may be implemented by amemory controller or its components as described herein. For example,the operations of method 600 may be performed by a snapback eventdetector as described with reference to FIG. 5. In some examples, amemory controller may execute a set of instructions to control thefunctional elements of the snapback event detector to perform thefunctions described below. Additionally or alternatively, a memorycontroller may perform aspects of the functions described below usingspecial-purpose hardware.

At 605, the memory controller may apply, during a write operation, afirst pulse having a first polarity to a memory cell storing a firstlogic state. The operations of 605 may be performed according to themethods described herein. In some examples, aspects of the operations of605 may be performed by an application component as described withreference to FIG. 5.

At 610, the memory controller may detect a snapback event at the memorycell in response to applying the first pulse. The operations of 610 maybe performed according to the methods described herein. In someexamples, aspects of the operations of 610 may be performed by adetection component as described with reference to FIG. 5.

At 615, the memory controller may apply a second pulse having a secondpolarity different than the first polarity to the memory cell inresponse to detecting the snapback event. The operations of 615 may beperformed according to the methods described herein. In some examples,aspects of the operations of 615 may be performed by an applicationcomponent as described with reference to FIG. 5.

At 620, the memory controller may store a second logic state differentthan the first logic state in the memory cell based on applying thesecond pulse to the memory cell. The operations of 620 may be performedaccording to the methods described herein. In some examples, aspects ofthe operations of 620 may be performed by a storage component asdescribed with reference to FIG. 5.

FIG. 7 shows a flowchart illustrating a method 700 that supportstechniques for programming memory cell in accordance with aspects of thepresent disclosure. The operations of method 700 may be implemented by amemory controller or its components as described herein. For example,the operations of method 700 may be performed by a snapback eventdetector as described with reference to FIG. 5. In some examples, amemory controller may execute a set of instructions to control thefunctional elements of the snapback event detector to perform thefunctions described below. Additionally or alternatively, a memorycontroller may perform aspects of the functions described below usingspecial-purpose hardware.

At 705, the memory controller may apply, during a write operation, afirst pulse having a first polarity to a memory cell storing a firstlogic state. The operations of 705 may be performed according to themethods described herein. In some examples, aspects of the operations of705 may be performed by an application component as described withreference to FIG. 5.

At 710, the memory controller may detect the first logic state stored bythe memory cell in response to applying the first pulse to the memorycell. The operations of 710 may be performed according to the methodsdescribed herein. In some examples, aspects of the operations of 710 maybe performed by a detection component as described with reference toFIG. 5.

At 715, the memory controller may store a second logic state in thememory cell by applying a second pulse having a second polarity duringthe write operation in response to detecting the first logic state,where the second logic state is different than the first logic state.The operations of 715 may be performed according to the methodsdescribed herein. In some examples, aspects of the operations of 715 maybe performed by a storage component as described with reference to FIG.5.

FIG. 8 shows a flowchart illustrating a method 800 that supportstechniques for programming memory cell in accordance with aspects of thepresent disclosure. The operations of method 800 may be implemented by amemory controller or its components as described herein. For example,the operations of method 800 may be performed by a snapback eventdetector as described with reference to FIG. 5. In some examples, amemory controller may execute a set of instructions to control thefunctional elements of the snapback event detector to perform thefunctions described below. Additionally or alternatively, a memorycontroller may perform aspects of the functions described below usingspecial-purpose hardware.

At 805, the memory controller may reduce, for a duration, a thresholdvoltage of a memory cell during a write operation by applying a firstpulse to the memory cell having a first polarity, the memory cellincluding a first logic value. The operations of 805 may be performedaccording to the methods described herein. In some examples, aspects ofthe operations of 805 may be performed by a reduction component asdescribed with reference to FIG. 5.

At 810, the memory controller may apply, during the duration, a secondpulse to the memory cell during the write operation, the second pulsehaving a second polarity different than the first polarity. Theoperations of 810 may be performed according to the methods describedherein. In some examples, aspects of the operations of 810 may beperformed by an application component as described with reference toFIG. 5.

At 815, the memory controller may store a second logic value in thememory cell after applying the second pulse. The operations of 815 maybe performed according to the methods described herein. In someexamples, aspects of the operations of 815 may be performed by a storagecomponent as described with reference to FIG. 5.

A method is described. In some examples, the method may includeapplying, during a write operation, a first pulse having a firstpolarity to a memory cell storing a first logic state. In some examples,the method may include detecting a snapback event at the memory cell inresponse to applying the first pulse. The method may include applying asecond pulse having a second polarity different than the first polarityto the memory cell in response to detecting the snapback event. Themethod may include storing a second logic state different than the firstlogic state in the memory cell based at least in part on applying thesecond pulse to the memory cell. In some examples, the method mayinclude applying a first voltage to a first access line coupled with thememory cell. The method may include applying a second voltage to asecond access line coupled with the memory cell, wherein applying thefirst pulse is based at least in part on applying the first voltage andthe second voltage.

The method may include applying the second voltage to the first accessline. The method may include applying the first voltage to the secondaccess line, wherein applying the second pulse is based at least in parton applying the first voltage to the second access line and the secondvoltage to the first access line. In some examples, the method mayinclude detecting a reduction in a magnitude of a voltage across thememory cell, wherein detecting the snapback event is based at least inpart on detecting the reduction in the magnitude of the voltage. In someexamples, the snapback event is based at least in part on a value of thefirst logic state being different than the value of the second logicstate to be stored to the memory cell. In some examples, the method mayinclude selecting a voltage magnitude of the first pulse based at leastin part on a value of the second logic state to be stored to the memorycell.

In some examples, a threshold voltage of the memory cell is reducedbased at least in part on applying the first pulse. In some examples,the reduced threshold voltage of the memory cell is based at least inpart on the first logic state. In some examples, a magnitude of thethreshold voltage of the memory cell is reduced for a duration inresponse to the occurrence of the snapback event. In some examples, thesecond pulse is applied to the memory cell during the duration when thethreshold voltage is reduced. In some examples, the method may includeperforming, during the duration, a read operation or an additional writeoperation on the memory cell. In some examples, the second pulse may beapplied after the duration. In some examples, operations other than awrite operation may occur between the first pulse and the second pulse.In some examples, the method may include detecting a second snapbackevent at the memory cell in response to applying the second pulse to thememory cell after the duration. In some examples, the reduced thresholdvoltage of the memory cell is based at least in part on the first logicstate. In some examples, the memory cell comprises a self-selectingmemory cell.

In some examples, a threshold refresh operation may occur by selectingthe memory cell after the duration in either polarity without completingthe write operation. In some examples, when the memory cell isdeselected, additional snapback events or other array operations may beconducted on other portions of the memory array before completing thewrite operation.

An apparatus is described. In some examples, the apparatus may supportmeans for applying, during a write operation, a first pulse having afirst polarity to a memory cell storing a first logic state. Theapparatus may support means for detecting a snapback event at the memorycell in response to applying the first pulse. The apparatus may supportmeans for applying a second pulse having a second polarity differentthan the first polarity to the memory cell in response to detecting thesnapback event. The apparatus may support means for storing a secondlogic state different than the first logic state in the memory cellbased at least in part on applying the second pulse to the memory cell.The apparatus may support means for applying a first voltage to a firstaccess line coupled with the memory cell. The apparatus may supportmeans for applying a second voltage to a second access line coupled withthe memory cell, wherein applying the first pulse is based at least inpart on applying the first voltage and the second voltage.

The apparatus may support means for applying the second voltage to thefirst access line. The apparatus may support means for applying thefirst voltage to the second access line, wherein applying the secondpulse is based at least in part on applying the first voltage to thesecond access line and the second voltage to the first access line. Theapparatus may support means for detecting a reduction in a magnitude ofa voltage across the memory cell, wherein detecting the snapback eventis based at least in part on detecting the reduction in the magnitude ofthe voltage. The apparatus may support means for selecting a voltagemagnitude of the first pulse based at least in part on a value of thesecond logic state to be stored to the memory cell. The apparatus maysupport means for detecting a second snapback event at the memory cellin response to applying the second pulse to the memory cell after theduration.

A method is described. In some examples, the method may includeapplying, during a write operation, a first pulse having a firstpolarity to a memory cell storing a first logic state. The method mayinclude detecting the first logic state stored by the memory cell inresponse to applying the first pulse to the memory cell. The method mayinclude storing a second logic state in the memory cell by applying asecond pulse having a second polarity during the write operation inresponse to detecting the first logic state, wherein the second logicstate is different than the first logic state. The method may includeapplying a first voltage to a first access line coupled with the memorycell. The method may include applying a second voltage to a secondaccess line coupled with the memory cell, wherein applying the firstpulse is based at least in part on applying the first voltage and thesecond voltage.

In some examples, a threshold refresh operation may occur by selectingthe memory cell after the duration in either polarity without completingthe write operation. In some examples, when the memory cell isdeselected, additional snapback events or other array operations may beconducted on other portions of the memory array before completing thewrite operation.

In some examples, applying the first voltage to the first access linereduces a threshold voltage of the memory cell. In some examples, thesecond voltage is greater than the reduced threshold voltage of thememory cell. In some examples, detecting the first logic state is basedat least in part on a threshold voltage of the memory cell being lessthan a magnitude of the first pulse. In some examples, storing thesecond logic state to the memory cell is based at least in part on athreshold voltage of the memory cell being reduced for a duration. Insome examples, the first polarity is opposite of the second polarity. Insome examples, the first logic state is detected during a duration afterapplying the first pulse, and wherein the second logic state is writtento the memory cell during the duration. In some cases, operations otherthan a write operation may be performed during the duration and/orbefore the second logic state is written to the memory cell.

An apparatus is described. In some examples, the apparatus may supportmeans for applying, during a write operation, a first pulse having afirst polarity to a memory cell storing a first logic state. Theapparatus may support means for detecting the first logic state storedby the memory cell in response to applying the first pulse to the memorycell. The apparatus may support means for storing a second logic statein the memory cell by applying a second pulse having a second polarityduring the write operation in response to detecting the first logicstate, wherein the second logic state is different than the first logicstate. The apparatus may support means for applying a first voltage to afirst access line coupled with the memory cell. The apparatus maysupport means for applying a second voltage to a second access linecoupled with the memory cell, wherein applying the first pulse is basedat least in part on applying the first voltage and the second voltage.

A method is described. In some examples, the method may includereducing, for a duration, a threshold voltage of a memory cell during awrite operation by applying a first pulse to the memory cell having afirst polarity, the memory cell comprising a first logic value. Themethod may include applying, during the duration, a second pulse to thememory cell during the write operation, the second pulse having a secondpolarity different than the first polarity. The method may includestoring a second logic value in the memory cell after applying thesecond pulse. The method may include determining the first logic valueof the memory cell based at least in part on reducing the thresholdvoltage of the memory cell during the write operation. In some cases,the first logic value of the memory may be determined before the writeoperation is complete.

The method may include reducing, after the duration, the thresholdvoltage of the memory cell during the write operation by applying thefirst pulse to the memory cell having the first polarity, the memorycell comprising the second logic value. In some examples, a magnitude ofthe second pulse applied to the memory cell is less than a magnitude ofthe first pulse. In some examples, the first pulse applies a voltageacross the memory cell in a first direction and the second pulse appliesa voltage across the memory cell in a second direction.

An apparatus is described. In some examples, the apparatus may supportmeans for reducing, for a duration, a threshold voltage of a memory cellduring a write operation by applying a first pulse to the memory cellhaving a first polarity, the memory cell comprising a first logic value.The apparatus may support means for applying, during the duration, asecond pulse to the memory cell during the write operation, the secondpulse having a second polarity different than the first polarity. Theapparatus may support means for storing a second logic value in thememory cell after applying the second pulse. The apparatus may supportmeans for determining the first logic value of the memory cell based atleast in part on reducing the threshold voltage of the memory cellduring the write operation. The apparatus may support means forreducing, after the duration, the threshold voltage of the memory cellduring the write operation by applying the first pulse to the memorycell having the first polarity, the memory cell comprising the secondlogic value.

It should be noted that the methods described above describe possibleimplementations, and that the operations and the steps may be rearrangedor otherwise modified and that other implementations are possible.Further, aspects from two or more of the methods may be combined.

Information and signals described herein may be represented using any ofa variety of different technologies and techniques. For example, data,instructions, commands, information, signals, bits, symbols, and chipsthat may be referenced throughout the above description may berepresented by voltages, currents, electromagnetic waves, magneticfields or particles, optical fields or particles, or any combinationthereof. Some drawings may illustrate signals as a single signal;however, it will be understood by a person of ordinary skill in the artthat the signal may represent a bus of signals, where the bus may have avariety of bit widths.

The term “electronic communication” and “coupled” refer to arelationship between components that support electron flow between thecomponents. This may include a direct connection between components ormay include intermediate components. Components in electroniccommunication or coupled to one another may be actively exchangingelectrons or signals (e.g., in an energized circuit) or may not beactively exchanging electrons or signals (e.g., in a de-energizedcircuit) but may be configured and operable to exchange electrons orsignals upon a circuit being energized. By way of example, twocomponents physically connected via a switch (e.g., a transistor) are inelectronic communication or may be coupled regardless of the state ofthe switch (i.e., open or closed).

As used herein, the term “substantially” means that the modifiedcharacteristic (e.g., a verb or adjective modified by the termsubstantially) need not be absolute but is close enough so as to achievethe advantages of the characteristic.

As used herein, the term “electrode” may refer to an electricalconductor, and in some cases, may be employed as an electrical contactto a memory cell or other component of a memory array. An electrode mayinclude a trace, wire, conductive line, conductive layer, or the likethat provides a conductive path between elements or components of memoryarray 102.

The devices discussed herein, including memory array, may be formed on asemiconductor substrate, such as silicon, germanium, silicon-germaniumalloy, gallium arsenide, gallium nitride, etc. In some cases, thesubstrate is a semiconductor wafer. In other cases, the substrate may bea silicon-on-insulator (SOI) substrate, such as silicon-on-glass (SOG)or silicon-on-sapphire (SOP), or epitaxial layers of semiconductormaterials on another substrate. The conductivity of the substrate, orsub-regions of the substrate, may be controlled through doping usingvarious chemical species including, but not limited to, phosphorous,boron, or arsenic. Doping may be performed during the initial formationor growth of the substrate, by ion-implantation, or by any other dopingmeans.

The description set forth herein, in connection with the appendeddrawings, describes example configurations and does not represent allthe examples that may be implemented or that are within the scope of theclaims. The term “exemplary” used herein means “serving as an example,instance, or illustration,” and not “preferred” or “advantageous overother examples.” The detailed description includes specific details forthe purpose of providing an understanding of the described techniques.These techniques, however, may be practiced without these specificdetails. In some instances, well-known structures and devices are shownin block diagram form to avoid obscuring the concepts of the describedexamples.

In the appended figures, similar components or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If just the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

Information and signals described herein may be represented using any ofa variety of different technologies and techniques. For example, data,instructions, commands, information, signals, bits, symbols, and chipsthat may be referenced throughout the above description may berepresented by voltages, currents, electromagnetic waves, magneticfields or particles, optical fields or particles, or any combinationthereof.

The various illustrative blocks and modules described in connection withthe disclosure herein may be implemented or performed with ageneral-purpose processor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. Ageneral-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices (e.g., a combinationof a DSP and a microprocessor, multiple microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration).

The functions described herein may be implemented in hardware, softwareexecuted by a processor, firmware, or any combination thereof. Ifimplemented in software executed by a processor, the functions may bestored on or transmitted over as one or more instructions or code on acomputer-readable medium. Other examples and implementations are withinthe scope of the disclosure and appended claims. For example, due to thenature of software, functions described above can be implemented usingsoftware executed by a processor, hardware, firmware, hardwiring, orcombinations of any of these. Features implementing functions may alsobe physically located at various positions, including being distributedsuch that portions of functions are implemented at different physicallocations. Also, as used herein, including in the claims, “or” as usedin a list of items (for example, a list of items prefaced by a phrasesuch as “at least one of” or “one or more of”) indicates an inclusivelist such that, for example, a list of at least one of A, B, or C meansA or B or C or AB or AC or BC or ABC (i.e., A and B and C). Also, asused herein, the phrase “based on” shall not be construed as a referenceto a closed set of conditions. For example, an exemplary step that isdescribed as “based on condition A” may be based on both a condition Aand a condition B without departing from the scope of the presentdisclosure. In other words, as used herein, the phrase “based on” shallbe construed in the same manner as the phrase “based at least in parton.”

Computer-readable media includes both non-transitory computer storagemedia and communication media including any medium that facilitatestransfer of a computer program from one place to another. Anon-transitory storage medium may be any available medium that can beaccessed by a general purpose or special purpose computer. By way ofexample, and not limitation, non-transitory computer-readable media cancomprise RAM, ROM, electrically erasable programmable read only memory(EEPROM), compact disk (CD) ROM or other optical disk storage, magneticdisk storage or other magnetic storage devices, or any othernon-transitory medium that can be used to carry or store desired programcode means in the form of instructions or data structures and that canbe accessed by a general-purpose or special-purpose computer, or ageneral-purpose or special-purpose processor. Also, any connection isproperly termed a computer-readable medium. For example, if the softwareis transmitted from a website, server, or other remote source using acoaxial cable, fiber optic cable, twisted pair, digital subscriber line(DSL), or wireless technologies such as infrared, radio, and microwave,then the coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared, radio,and microwave are included in the definition of medium. Disk and disc,as used herein, include CD, laser disc, optical disc, digital versatiledisc (DVD), floppy disk and Blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Combinations of the above are also included within the scope ofcomputer-readable media.

The description herein is provided to enable a person skilled in the artto make or use the disclosure. Various modifications to the disclosurewill be readily apparent to those skilled in the art, and the genericprinciples defined herein may be applied to other variations withoutdeparting from the scope of the disclosure. Thus, the disclosure is notlimited to the examples and designs described herein, but is to beaccorded the broadest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. A method, comprising: applying, during a writeoperation, a first pulse having a first polarity to a memory cellstoring a first logic state; detecting the first logic state stored bythe memory cell in response to applying the first pulse to the memorycell; and storing a second logic state in the memory cell by applying asecond pulse having a second polarity during the write operation inresponse to detecting the first logic state, wherein the second logicstate is different than the first logic state.
 2. The method of claim 1,further comprising: applying a first voltage to a first access linecoupled with the memory cell; and applying a second voltage to a secondaccess line coupled with the memory cell, wherein applying the firstpulse is based at least in part on applying the first voltage and thesecond voltage.
 3. The method of claim 2, wherein applying the firstvoltage to the first access line reduces a threshold voltage of thememory cell.
 4. The method of claim 3, wherein the second voltage isgreater than the reduced threshold voltage of the memory cell.
 5. Themethod of claim 1, wherein detecting the first logic state is based atleast in part on a threshold voltage of the memory cell being less thana magnitude of the first pulse.
 6. The method of claim 1, whereinstoring the second logic state to the memory cell is based at least inpart on a threshold voltage of the memory cell being reduced for aduration.
 7. The method of claim 1, wherein the first polarity isopposite of the second polarity.
 8. The method of claim 1, wherein thefirst logic state is detected during a duration after applying the firstpulse, and wherein the second logic state is written to the memory cellduring the duration.
 9. An apparatus, comprising: a first access linecoupled with a memory cell storing a first logic state; a second accessline coupled with the memory cell; and a memory controller coupled withthe first access line and the second access line, the memory controllerconfigured to: apply, during a write operation, a first pulse having afirst polarity to the memory cell during; detect the first logic statestored by the memory cell in response to applying the first pulse to thememory cell; and store a second logic state in the memory cell byapplying a second pulse having a second polarity during the writeoperation based at least in part detecting the first logic state,wherein the second logic state is different than the first logic state.10. The apparatus of claim 9, wherein the memory controller is operableto apply the first pulse having the first polarity to the memory cellduring a duration.
 11. The apparatus of claim 10, wherein the firstlogic state is detected during the duration and the second logic stateis written to the memory cell during the duration.
 12. The apparatus ofclaim 9, wherein: applying the first pulse having the first polaritycomprises applying a first voltage to the first access line; andapplying the second pulse having the second polarity comprises applyinga second voltage to the second access line, wherein writing the secondlogic state to the memory cell is based at least in part on a magnitudeof the second voltage exceeding a threshold voltage of the memory cell.13. The apparatus of claim 9, wherein the memory controller is operableto select the first pulse from a plurality of pulses based at least inpart on a value of the second logic state to be written to the memorycell.
 14. A non-transitory computer-readable medium storing codecomprising instructions which, when executed by a processor of anelectronic device, cause the electronic device to: apply, during a writeoperation, a first pulse having a first polarity to a memory cellstoring a first logic state; detect the first logic state stored by thememory cell in response to applying the first pulse to the memory cell;and store a second logic state in the memory cell by applying a secondpulse having a second polarity during the write operation in response todetecting the first logic state, wherein the second logic state isdifferent than the first logic state.
 15. The non-transitorycomputer-readable medium of claim 14, wherein the instructions, whenexecuted by the processor of the electronic device, further cause theelectronic device to: apply a first voltage to a first access linecoupled with the memory cell; and apply a second voltage to a secondaccess line coupled with the memory cell, wherein applying the firstpulse is based at least in part on applying the first voltage and thesecond voltage.
 16. The non-transitory computer-readable medium of claim15, wherein applying the first voltage to the first access line reducesa threshold voltage of the memory cell.
 17. The non-transitorycomputer-readable medium of claim 14, wherein detecting the first logicstate is based at least in part on a threshold voltage of the memorycell being less than a magnitude of the first pulse.
 18. Thenon-transitory computer-readable medium of claim 14, wherein storing thesecond logic state to the memory cell is based at least in part on athreshold voltage of the memory cell being reduced for a duration. 19.The non-transitory computer-readable medium of claim 14, wherein thefirst polarity is opposite of the second polarity.
 20. Thenon-transitory computer-readable medium of claim 14, wherein the firstlogic state is detected during a duration after applying the firstpulse, and wherein the second logic state is written to the memory cellduring the duration.